1. Related Applications and Patents
This invention is related to our application Ser. No. 244,099 filed Jan. 12, 1981 for "A Method of Making Constant Bonding Wire Tail Lengths".
2. Field of the Invention
The present invention is related to fine wire bonding and the operation of high speed automatic wire bonding machines. More particularly, the present invention is related to a novel method of making the bent end of the fine wire at the second bond in a direction which is optimized and oriented under the working face of a capillary fine wire bonding tool in preparation for a new first bond.
3. Description of the Prior Art
Fine wires of gold and aluminum are employed in wire bonding machines to make electrical interconnections between two or more electrodes on semiconductor devices. The most common wire interconnection made on a semiconductor is made between the conductive pad on a semiconductor chip and a conductive terminal which is adjacent the chip and which serves as an output lead to the connector pins of the package in which the semiconductor chip is contained.
Integrated circuit chips that have large numbers of pads must be connected to the lead out terminals that are arranged in some irregular pattern closely adjacent the outer perimeter of the semiconductor chip. When making the fine wire interconnections, it is a preferred practice to make the first bond on the very small conductive pad on the semiconductor chip. After forming a loop with the fine wire, a second bond is made on the conductive terminal. The fine wire is then severed by tearing or breaking the fine wire at the second bond. When the automatic wire bonder is a ball bonder, the wire is pulled vertically upward to sever it at the second bond and leave the wire unbent so it may be extended from the capillary bonding tool a predetermined length. The predetermined length of fine wire extending vertically from the capillary bonding tool is then heated by a hot gas such as hydrogen which causes the fine wire to make a ball on the end of the wire. This ball is then ball bonded to the next conductive pad on the semiconductor chip to be bonded and the next interconnection is made. Automatic ball bonders, such as that shown and described in U.S. Pat. No. 4,266,710 are provided with moveable X-Y tables and a bonding head which is pivoted from the main frame of the bonding machine.
When the fine wire interconnection is being made by an automatic wedge bonder such as that shown in U.S. Pat. No. 4,239,144, the wire is severed at the second bond by pulling the wire horizontally and vertically to break the wire at the second bond and leave the fine wire tail bent and oriented under the working face of the wedge bonding tool. The automatic wire bonder shown in U.S. Pat. No. 4,239,144 is provided with a rotary head and may be employed to perform the method set forth in our co-pending application Ser. No. 244,099.
Heretofore, wedge bonding tools have been provided with very narrow working faces. Heretofore, when such bonding wedges are employed to make a last bond (second bond), the bonding wedge preferably continues away from the last bond in a direction which is substantially aligned with the direction of the wire interconnection. This assures that the fine wire will be oriented under the narrow working face of the bonding wedge after it is broken. Once the tail or bent end of the fine wire is oriented under the bonding wedge, either the bonding wedge or the mechanism which supports the semiconductor being bonded must be rotated to align the wire bonding tail for the next bond. The chip may be mounted on a rotary platform or the bonding head may be mounted on a rotary head supporting frame as shown in U.S. Pat. No. 4,239,144.
If the rotary direction of movement mechanism is eliminated from such wedge bonding machines, they may be made cheaper and operated faster.
For reasons of both economy and speed of operation, semiconductor chips are being made smaller and the pads on such integrated circuits are being made smaller. Automatic wire bonders are employing smaller fine wires and are attempting to orient the tail or bent end of the fine wire under the working face of a wedge bonding tool so that it can exactly locate the small conductive pads on such integrated circuits. It has been found that the bonding wire tail under a wedge bonding tool has a tendency to miss the conductive pad on said semiconductors. Most high volume semiconductor chips are being wire bonded by computer controlled automatic wire bonders such as the Models 1418-1419 and 1470 made by Kulicke and Soffa Industries, Inc. of Horsham, Pa.
It has been a preferred practice to employ fine wire wedge bonding tools with a narrow face when making fine wire interconnections with aluminum wire. Aluminum ball bonding machines are commercially available, however, there are numerous problems which result from attempting to ball bond aluminum wires which present problems heretofore unsolved.
It would be desirable to provide a method of wedge bonding which would allow the use of aluminum wires to make interconnections and which would not require a rotary head or rotary substrate support for making such aluminum fine wire interconnections. Further, it would be desirable that the method of making aluminum fine wire interconnections would be applicable to gold wires so that one automatic bonding machine could be used for making both aluminum and gold fine wire interconnections.